Date   

Re: Another A5 board repair attemp - help needed

Rogerio O
 

As I have posted before I shorted some U2521 pins while trying to measure its outputs whith a scope probe.
Immediately after that the + 1.36V and -1.25V voltages references dropped to values close to zero.
So I guess I have fried U2521.
For the ones following this topic I have uploaded an image of the voltages at the DAC input to the album A5 repair attempt (https://groups.io/g/TekScopes/album?id=256231).
Before doing that I made a continuity check on all traces of this resistor divider and all were ok.
The measurements show that there is about 1mA of current and it is going all to pin 14, but I don't known if this is how the circuit is supposed to work.
I tried to check these values posted in old trends as images but apparently they were were lost when this group moved so I will post the values here as well.
+10V input --- 10.000V
R2026 --- 1.035V
R2013 --- 8.96V
R2011 --- 0.66V
R2015 --- 8.30V
R2014 --- 8.30V
R2010 (fully CCW - wiper contacting R2013) --- 0.004V
R2012 --- 0.002V


Photo Voltages at DAC divider.jpg uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the A5 repair attempt album of the TekScopes@groups.io group.

By: Rogerio O


Re: 7A12 attenuator board clone

Göran Krusell
 

Mathematically it is not possible to compensate for this problem and the reason is that the dielectric constant is frequency dependent - and this is bad.
Göran


Re: Tek 475 Front Panel Ground Point

Colin Herbert
 

I have just undertaken a voyage of discovery amongst my various bits and pieces and not only do I have one of these, but it is shown in my 475A Service Manual as "Plug, Tip: W/Binding Post" in the "Accessories" section. Oddly enough, though, I can't (at present) find it in my 468 Manual, which come in two parts, nor in the Common Design Parts catalogues. I suppose that with the 475 that was your father's, there is one of these in the earth-point socket that I mentioned that both of my 475As have.

Now if only I could find the bits that I was actually looking for.....

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jeff Dutky
Sent: 14 November 2020 19:18
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 475 Front Panel Ground Point

Dave, Colin,

Thanks for the replies. I also found (and lost the auction for) a 475A on eBay that showed the ground wire adapter in a bag of "accessories" so it was clear that this was original equipment. Differential measurements seems a very likely suggestion considering that my father was a service engineer for a manufacturer of mass analysis and associated equipment when he got and used this scope.


Re: 7A12 attenuator board clone

Dave Wise
 

I saw this in my 1A7. I reduced the common-mode error by replacing one resistor in the attenuator with a smaller R in series with a parallel RC. Values were cut and try.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Tom Lee via groups.io <tomlee=ee.stanford.edu@groups.io>
Sent: Saturday, November 14, 2020 12:53 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7A12 attenuator board clone

The "hook" that people have mentioned a couple of times is the nickname
for the step response artifact caused by a dispersive dielectric. If you
adjust the compensation so that the rising edge peaks at the same level
as the steady-state value, you find that the response sags in between.
There are ways to compensate for that effect to one degree or another,
but it's not trivial to do it well.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/13/2020 13:06, Martin Hodge wrote:
According to the manual, the 7A12 attenuator board is made of Polyphenylene Oxide. If one were to try to use a 7A12 with an FR4 attenuator, how would it's inferiority manifest on the screen? And what signal would one need to feed it to make it "fail"?

In case I didn't make it clear, this was a purely educational endeavor for me. I was curious to see what the difference would be, if any.





Re: Tek 475 Front Panel Ground Point

 

Dave, Colin,

Thanks for the replies. I also found (and lost the auction for) a 475A on eBay that showed the ground wire adapter in a bag of "accessories" so it was clear that this was original equipment. Differential measurements seems a very likely suggestion considering that my father was a service engineer for a manufacturer of mass analysis and associated equipment when he got and used this scope.


Added Folder /pickup devices for vey-low-frequency reception #file-notice

TekScopes@groups.io Notification <noreply@...>
 

snapdiode added folder /pickup devices for vey-low-frequency reception


#file-notice A scan of an old article #file-notice

snapdiode
 

I just scanned in something that looks like the structure inside the P6042 head.

I am puzzled why scanners don't have a "flip every other page" option, when you scan a book you have no choice but to flip it over every other page...


Re: Curve tracer as a power supply

 

With this problem, I always use my Variac to generate sufficient AC voltage to the input of any DUT, noting the minimum VAC it takes to activate the DUT.
Absolutely ZERO guesswork, when using this method.

Then I look over here for Amveco Toroid Transformers, which match (+/-) the required VAC (which I discovered on the Variac).
https://www.surplussales.com/class/inductor/toroidal.html

You can certainly select up to about 20% more VAC capability with no adverse effects, except for a little warmth in the PSU circuit.
Toroids have far less loss factor than E or C type transformers, therefore generate far less heat.

Menahem Yachad
CondorAudio
Jerusalem


Re: Tek 475 Front Panel Ground Point

Daveolla
 

At 10:25 PM 11/04/2020, you wrote:
I have two scopes of my father's, one 475 and one 2213. The ground point on the front panel of the 2213 is just a banana plug socket, but on the 475 the ground point is a knurled metal post (looks like nickel). This always puzzled me because the post could turn, but didn't seem to unscrew, and it is much too big to attach a ground clip from a probe, or do much of anything else with. Well, today I solved part of the mystery of this odd ground point: it's a separate banana plug with screw-down terminal!
lar part (assuming that it's a generic piece of kit) with little success, but I may not be using the right search terms.

Does anybody know if Tek shipped such an accessory as part of the stock 475?
Yup,I (banana plug with small knurled end) have one and it is listed in the Tek 468 Scope manual as; "adapter, Ground Wire .......134-0016-01"
So you finally decided to give the post a pull ......................sorry, I had been meaning to suggest that to you:(

Dave




Re: Tek 475 Front Panel Ground Point

Colin Herbert
 

I have two 475As and neither have anything like you describe. They both have an banana-socket earth-point just to the left of the bottom left screw holding the CRT bezel in place. However, I have a couple of 7000-series plugins (7A13 & 7A22) which have earthed metal binding-posts with banana-plug sockets, where the knurled "nut" will unscrew completely and expose a hole drilled laterally across the metal post. These two plug-ins are capable of differential measurement between two inputs and I would guess that this earth-point is necessary for differential measurements. Perhaps your father was attempting to do differential measurements using the two channels on the 475 with one channel switched to "invert". If you look up info on differential measurements and how to make the connections, it might be a bit clearer.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jeff Dutky
Sent: 05 November 2020 04:25
To: TekScopes@groups.io
Subject: [TekScopes] Tek 475 Front Panel Ground Point

I have two scopes of my father's, one 475 and one 2213. The ground point on the front panel of the 2213 is just a banana plug socket, but on the 475 the ground point is a knurled metal post (looks like nickel). This always puzzled me because the post could turn, but didn't seem to unscrew, and it is much too big to attach a ground clip from a probe, or do much of anything else with. Well, today I solved part of the mystery of this odd ground point: it's a separate banana plug with screw-down terminal!

I went on the web looking for any images of a Tek 475 with this banana plug in the ground port, and I can't find a single one. I don't know why this never occurred to me before now, except that the ground point is rarely mentioned in Tek documentation (it doesn't even get it's own numbered label in the 475 Operators Manual), and the knurled post doesn't photograph very noticeably, no more so than an empty banana plug socket. I suspect that my father added this (possibly generic) banana plug to his scope as some convenience of his own (not sure what that would be, though: I had to use pliers to loosen the knurled nut, and the revealed contact faces, post and hole show no obvious signs of use), but he didn't add a similar piece to his 2213, so I'm at a loss for a sensible explanation.

I've tried to search Amazon for a similar part (assuming that it's a generic piece of kit) with little success, but I may not be using the right search terms.

Does anybody know if Tek shipped such an accessory as part of the stock 475?


Re: Peter Keller CRT Articles and Book. WAS: Reworked Tek' Lit

Colin Herbert
 

Well, I was just quoting from this message:

"Just DL the complete book in PDF at this site; https://archive.org/details/keller1991cathode-ray/mode/2up
It´s opensource so free for everyone :-)

René"

This was on Tekscopes a while ago:
https://groups.io/g/TekScopes/message/172365

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Roy Thistle
Sent: 13 November 2020 20:00
To: TekScopes@groups.io
Subject: Re: [TekScopes] Peter Keller CRT Articles and Book. WAS: Reworked Tek' Lit

On Fri, Nov 13, 2020 at 08:27 AM, Colin Herbert wrote:


It is open-source
but... is it?
Google Books still shows it as copyrighted Palisades Press... (which probably means Mr. Keller has the copyright?)
It's also for sale on Amazon, through some used book reseller.


Re: Peter Keller CRT Articles and Book. WAS: Reworked Tek' Lit

Tam Hanna
 

Hello Dennis,

I have tried to e-mail you offlist multiple times asking for the dude's contact data, but got nothing.


Can you please send it to me?


Tam

--
- - - - -
With best regards
Tam HANNA

Enjoy electronics? Join 13500 followers by visiting the Crazy Electronics Lab at https://www.instagram.com/tam.hanna/


Re: Another A5 board repair attemp - help needed

Siggi
 

Þann lau., 14. nóv. 2020 kl. 05:32 skrifaði Rogerio O <rodd414@gmail.com>:

Since I will have to wait for the Mouser parts to arrive, I intend to
follow your suggestion to measure the voltages drop across the DAC
resistors.
Can I turn the scope on without U2521/U2420 soldered in place?

The only damage that could happen is CRT burn. If the beam intensity is
still under control or low/none, you’re fine. If the beam is too bright, it
helps to defocus it, and you can always turn down the CRT bias.


Re: 7L5 Res shaft encoder

Jean-Paul
 


Re: Another A5 board repair attemp - help needed

Rogerio O
 

Since I will have to wait for the Mouser parts to arrive, I intend to follow your suggestion to measure the voltages drop across the DAC resistors.
Can I turn the scope on without U2521/U2420 soldered in place?
Thanks


Re: 7L5 Res shaft encoder

Jean-Paul
 

Rebonjour, many thanks for the tip on knob/encoder removal.

I have a second unit that is much worse, on both shaft encoders, I shall try the right angle PosiDrive to remove the encoders.

The original TEK service manual reveals the knobs are just switches, circular PCB and wipers. No shaft encoder!
Pressing the knob in/out or pushing the front panel can change it 5k><500K. Probably a single contact on the x1 x100 switch.
I washed with 99% iso alcohol, no change. Suspect oxidized connector on shaft encoder to front panel PCB.

Any other experienced TEK spec analyzer plugin experts out there?

Besides this fault, it tests 100%. Amazing for such a complex box that is ~40 years old!

Bon Journée a tous,

Jon

PS: With the nice large CRT of 7603, and a 7L12 + manual, I am in spectrum city.




.


Jon

PS: How difficult to swap an OPT 25 tracking between the two 7L5?


Re: 7A12 attenuator board clone

Tom Lee
 

The "hook" that people have mentioned a couple of times is the nickname for the step response artifact caused by a dispersive dielectric. If you adjust the compensation so that the rising edge peaks at the same level as the steady-state value, you find that the response sags in between. There are ways to compensate for that effect to one degree or another, but it's not trivial to do it well.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/13/2020 13:06, Martin Hodge wrote:
According to the manual, the 7A12 attenuator board is made of Polyphenylene Oxide. If one were to try to use a 7A12 with an FR4 attenuator, how would it's inferiority manifest on the screen? And what signal would one need to feed it to make it "fail"?

In case I didn't make it clear, this was a purely educational endeavor for me. I was curious to see what the difference would be, if any.




Re: Interesting scope on eBay. Hickok copy of 535 or Tektronix?

Jim Tibbits
 

Never saw a Lavoie when I was in USAF (61-65)..spent about a year and a
half curled up in the "wine celler" on the B-52 tweaking alignments on the
terrain avoidance computer with a trusty tek 545 tho

Jim

On Fri, Nov 13, 2020 at 4:54 PM Brad Thompson <brad.thompsonaa1ip@gmail.com>
wrote:

greenboxmaven via groups.io wrote on 11/13/2020 4:17 PM:

In my Air Force time 1969-73, the Lavoie clones were seen mostly at
training bases.
<snip>

Hello-- Suffering from a bad case of Tektronix lust in 1968 and not
having much cash, I bought a
bargain-priced Lavoie LA-259 (?) scope from a certain salvage yard in
Cambridge, MA. After
dragging the thing home, I discovered that its power supply had failed.
IIRC, its oddball power supply was built around a saturable
reactor/transformer
(memory fails me here).

So had the saturable reactor.

The word "unobtanium" hadn't been coined at the time, but it would have
applied in
this case.

73--

Brad AA1IP






Re: Interesting scope on eBay. Hickok copy of 535 or Tektronix?

greenboxmaven
 

The transformer was probably ferroresonant. It would compensate fairly well for line voltage variations, but would not regulate or stabilize the voltages produced by the secondary windings. Also, the power frequency has to be close to the design or the output of the transformer drops quickly. If the Lavoie used one of these transformers, it was almost certainly custom made and would have been very costly to replace.

Bruce Gentry, KA2IVY

On 11/13/20 7:53 PM, Brad Thompson wrote:
greenboxmaven via groups.io wrote on 11/13/2020 4:17 PM:

In my Air Force time 1969-73, the Lavoie clones were seen mostly at training bases.
<snip>

Hello-- Suffering from a bad case of Tektronix lust in 1968 and not having much cash, I bought a
bargain-priced Lavoie LA-259 (?) scope from a certain salvage yard in Cambridge, MA. After
dragging the thing home, I discovered that its power supply had failed.
IIRC, its oddball power supply was built around a saturable reactor/transformer
(memory fails me here).

So had the saturable reactor.

The word "unobtanium" hadn't been coined at the time, but it would have applied in
this case.

73--

Brad AA1IP




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